Electro-optical waveguides based on poled nonlinear optical (NLO) chromophore-polymer composites exhibit limited functionality when the uniform chromophore alignment achieved by poling is gradually lost due to a variety of relaxation processes attributed to the thermoplastic matrix. One approach to ameliorating this deficiency is to crosslink the polymer matrix after poling to “fix” the chromophore orientation. Various resins and crosslinking schemes have been developed with the aim of effecting an “on demand” cure triggered either thermally or by some other means after an initial processing step.
There are, however, a number of difficulties in effecting this transformation. First, the crosslinking reaction must not occur before or during poling, which is usually conducted at a temperature just above the glass transition temperature (Tg) of the polymer matrix. After poling, the crosslinking must be initiated either by raising the temperature or by some other form of initiation. Such a “command cure” feature is not easily accomplished.
A second difficulty in effecting an on demand cure by thermal or other means is that the crosslinking reaction of the polymer must be compatible with the NLO chromophore functionality. In particular, the dyes comprising NLO chromophores are generally highly conjugated molecules bearing both electron donor and electron acceptor functional groups. The complexity of these dyes thus renders them susceptible to undesirable side reactions. Conditions of most known thermally or photochemically-induced crosslinking reactions may undesirably give rise to reactions which alter the structure of the chromophore itself.
Therefore, there is a need in the art for polymer materials which exhibit complete crosslinking under sharply defined and relatively low temperature conditions.